Fibrous element



Aug. 26, 1969 R. C. HARRINGTON. JR, ETAL FIBROUS ELEMENT Original Filed July 22, 1964 O i F 1 Hunting f ponnq I ormnq aw g) Polyethylane Appllcoflon FIG.2.

ROBERT C. HARRINGTOMJR JAMES L. SMITH JAMES H. BOND INVENTOR. BY Q MM WWW ATTORNEYS I United States Patent FIBROUS ELEMENT Robert C. Harrington, Jr., James L. Smith, and James H. Bond, Kingsport, Tenn., assignors to Eastman Kodak Company, Rochester, N .Y., a corporation of New Jersey Continuation of application Ser. No. 521,474, Nov. 22, 1965, now PatentNo. 3,272,687, dated Sept. 13, 1966, which is a division of application Ser. No. 384,334, July 22, 1964. This. application July 24, 1967, Ser. No.

Int. CLB29l1 9/04; D04h 3/12 US. Cl. 156-152 2 Claims This application is a continuation of our application Ser. No. 521,474 filed Nov. 22, 1965, now abandoned, which was copending with and a division of our application Ser. No. 384,334 filed July 22, 1964, now US. vPatent 3,272,687, which was copending with and a continuation-in-part of application Ser. No. 157,212 filed Dec. 5, 1961, now US. Patent 3,229,008.

This invention relates to a non-woven fabric. More particularly, it concerns a polypropylene vapor permeable shaped object or fibrous element bonded'by polyethylene.

In our earlier application there has been described a process for converting fibro-plastic material substantially directly into fibrous materials such as non-woven fabrics, cable stuffing, cigarette filters and the like. The fibrous material'may be prepared by applying a stream of inert gas or steam propelled substantially at right angles to the extruded polymer melt or' solution, thereby attentuating the melt or solution into'the form of fibers which are collected in a direction substantially countercurrent to that of the propellent stream. Once an initial collecting point is provided, these fibers adhere in the form of tow which can be packaged in any suitable manner. This tow or fibrous material may be blended with certain other fibers in non-woven fabrics. However, because of the similarity of the relatively low melting points of both polypropylene and polyethylene and the similarity of many other chemicaland physical properties of each it has heretofore been unknown how to form a polypropylene non-woven fabric bonded with polyethylene as thus formed or by any other polyethylene. It is known that polyolefins in granular form may be used to cause bonding of dissimilar sheet materials by the application of heat, for example, laminated rayon nonwoven material bonded with polyethylene granules as disclosed in US. Patent 2,992,149. Nevertheless, to the best of our knowledge no method has as yet been devised whereby polypropylene tow may be formed into bonded vapor permeable fibrous element or non-woven fabric by using polyethylene as a bonding medium. Accordingly, it is believed apparent that the development of a polypropylene non-woven fabric bonded by polyethylene represents a highly desirable result.

It is an object of this invention, therefore, to disclose a novel polypropylene non-woven fabric bonded by polyethylene, yet still retaining its vapor-permeable characteristic. A further object is to disclose a simple and economical method of bonding polypropylene in the form of ice a non-woven fabric by the use of polyethylene as the bonding material. A still further object is to provide a non-woven fabric suitable for use in innerliners and inert filters. Other objects will appear hereinafter.

We have found that a non-woven material containing polypropylene can be bonded with a polyethylene binder to form a vapor permeable fibrous element. The bonding may be accomplished by the use of polyethylene which has a low melt viscosity at elevated temperatures. A characteristic of this polyethylene binder, especially when fibrous form is used, is its viscosity in the neighborhood of 8000 centipoises at 20 C. above its accepted flow point. By accepted flow point we mean ASTM D36-26 ring and ball softening point. The polyethylene used may be in fibrous or wax form. When a wax form of polyethyleneis used it should bean emulsifiable or watersoluble type. The polyethylene wax may be a partially oxidized low melting point polyethylene and may be blended with another wax such as paraffin.

While we do not wish to be bound by an particular theory as to why the desired bonding occurs, it appears that the above mentioned polyethylene characteristics or properties are necessary in order to have the polyethylene flow to the intersects of the polypropylene fiber and form bonds at these intersects such that a rigid vapor permeable object may be formed. Standard high density or low density polyethylene may be used or a similar degraded polyethylene. We have found especially useful polyethylene having a melting point in the neighborhood of C., for example, Eastmans Epolene C, a low-molecular weight polyethylene resin, or a similar degraded polyethylene having a melting point close to C. When fibers are used the denier per filament may vary from 1.5-200, although the preferred range is from about 2 to about 16. Mixtures of such fibers or waxes may be used to obtain any desired intermediate melting point, provided the characteristic low melt viscosity at elevated temperatures is exhibited. The polypropylene which may be bonded with polyethylene fibers in accordance with our invention may be either high-density or low-density polypropylene or blends of various polypropylenes, oriented and unoriented polypropylene, polypropylene resins or degraded polypropylene. The denier per filament may be from 1.5 to 200, although better bonding is generally achieved at a denier per filament of from about 2 to about 16.

The. polyethylene fiber-bonded polypropylene nonwoven fabric of this invention may be formed by blending batts of polypropylene and polyethylene on a card or other conventional equipment for producing non-woven material followed by subjection to heat with or without pressure. When polyethylene wax as bonding agent is used it may be added to polypropylene tow by spraying, dusting, or the like. Thus, a coherent, well-bonded mass of polypropylene fibers having high strength and rigidity in all directions is formed. An important advantage of such batts or fibrous bundles is that their density can be varied from a low to a very high figure, for example, from about 1 oz./sq. yd. 0/2" thick) to about 4 oz./sq. yd. /2" thick). When prepared by carding the variation in density to the desired amount may be accomplished simply by varying the degree of compression during the bonding operation.

A further understanding of our invention may be had by reference to the drawings of which:

FIG. 1 is a schematic diagram in flow sheet form illustrating the method of this invention for making a polypropylene fibrous element bonded with polyethylene, and

FIG. 2 is a schematic surface representation drawn to an enlarged scale of the fibrous product of this invention showing in detail the bonding of polypropylene at their intersects by the polyethylene.

In FIG. 2 the non-woven fabric of this invention is shown as a fibrous reticulated web wherein the polypropylene fibers are in a random or haphazard distribution with bonds clearly shown at a large number of their intersects. The polypropylene fibers bonded at their intersects by the polyethylene are shown to have not lost their identity in any way by the bonding.

The drawing depicts a vapor permeable fibrous web of bonded polypropylene fibers consisting of a plurality of randomly arranged polypropylene fibers 10 and a plurality of polyethylene bonds 12 at various intersects of said polypropylene fibers.

The following examples are illustrative of our invention.

Example I 60% by weight of d./f., 2" polypropylene fibers were mixed with 40% by weight of fibers from Epolene C resin (M.P. about 100 C.) having a denier per filament range from 2 to and cut 1%". This blend was formed into a card web having a weight of 1 oz./sq. yd. /z" thick). Hot air (130 C.) was blown through the batt for 5 minutes, after which it was allowed to cool. Microscopic examination showed the polypropylene to be bonded at many of the intersects and a very strong, light, foraminous structure was produced. FIGURE 1 shows the type of bonding produced.

Example II 60% by weight of 5 d./f., 2" polypropylene fibers were mixed with 40% by weight of Epolene C of the type described in Example I. This mixture was carded, and the resultant card web bonded by heating with 60 lb. steam under moderate pressure for 1 minute in a Hofiman press. The resulting batt was moderately dense and had good strength in all directions.

Example III 80% by weight of 5 d./f., 2" polypropylene fibers were mixed with by weight of Epolene C as described in Example I, and formed into a card web. This Web was then bonded under light pressure and heated from 60 lb. steam for 1 minute in a Hoffman press. The resulting batt was well bonded, had good strength in all directions, and weighed about 1 oz./sq. yd. /2" thick). This batt was used in innerliners to give good insulation.

Example IV A batt was made from 60% polypropylene fibers and 40% of a binder fiber prepared from a polyethylene wax having a melting point of 120 C. The batt was prepared in the manner as described in Example I except that bonding was accomplished at 140 C. The resulting nonwoven structure was of medium density, had good strength in all directions, and was able to withstand temperatures of 100 C. without mechanical deterioration.

Example V Another blend was prepared using 70% by weight of 5 d./f., 2" polypropylene fibers and by weight of fibers of a polyethylene wax having a melting point of 120 C. This web was calendered under 2000 lbs. pressure at 130 C. to produce a dense, strong polypropylene structure. It was used in battery separator plates with excellent solvent resistance.

Example VI Polyethylene having a specific gravity of 0.907 and a viscosity at 300 F. of approximately 9000 centipoises was extruded into a 32-oz. propellent stream directed at right angles thereto and the filaments formed by said propellent stream were collected as fibrous tow moving substantially counter-currently to the direction of said propellent stream. The fibrous tow contained filaments of a variable denier per filament of 4-20. A batt was prepared by blending 60% by weight of 8 d./f., 2" polypropylene 4 fibers with 40% by weight of the polyethylene tow. This blend was formed into a card web having a weight of 5 oz./sq. yd. (1" thick). Hot air (130 C.) was blown through the batt for 5 minutes after which it was allowed to cool. Microscopic examination showed that the polypropylene non-woven fabric was bonded at many of the filament intersects into a strong, light, forarninous structure.

Example VII A 60,000 total denier tow comprised of 20 d./f. round cross section polypropylene fibers was crimped to 12 crimps per inch and then heatset for.5 minutes at 125 C. The heatset tow was opened, sprayed with 5% solids from a 25 solids polyethylene wax emulsion and made into 24.8 mm. x 102 mm. filter rods. Twenty rods were heated in an oven for 3 minutes at C. The 20 heated rods along with 20 unheated and 20 control rods without binder were checked for hardness and pressure drop. The rod hardness values for the heated, unheated, and control rods were 6.90, 13.0, and 15.0 respectively. The pressure drops of the heated, unheated, and control rods were 3.1, 3.4, and 3.5 inches of water respectively. It will be noted from the above data that the presence of the polyethylene did not significantly effect rod pressure drop but did make a very significant improvement in rod hardness.

The bonded rods retained a high degree of rigidity, were easier cut, and produced a cleaner cut than did the unbonded rods. The pressure drop was determined by measuring the pressure diiferential required to produce an air flow through the filter of 1050 cc./ minute.

The rod hardness was determined by measuring the deformation of the rod when subjected to a sudden load of 347.5 grams. The lower hardness values represent the harder rods.

Example VIII A 65,000 total denier tow comprised of 20 d./f. round cross section polypropylene fibers was crimped to 12 crimps per inch and heatset for 5 minutes at 125 C. The crimped and heatset tow was opened and sprayed with 5% solids from a 25% solids polyethylene wax emulsion. The sprayed tow was made into 24.8 mm. x 102 mm. filter rods and heated for 0, /2, 3, and 5 minutes at 110 C. and 125 C. The treated rods were checked for hardness and pressure drop by the same methods described in Example VII. The results are tabulated below.

Bonding Bonding Sample Percent time in temp Rod Rod pres- N o. binder minutes hardness sure drop It will be noted from the above table that the maximum hardness value for these particular rods appears to be about 4.5. It will also be noted that this value is obtained after 5 minutes at 110 C. and after only 3 minutes at 125 C. This shows that bonding time here is a function of the bonding temperature and that these very low bonding times may be used if the bonding temperature is raised.

A hardness value of 9.2 is adequate for commercial processing. In the above table this value was obtained after only 30 seconds at 110 C.

Example IX A 60,000 total denier tow comprised of 5 d./f. round cross section polypropylene fibers was crimped to 16-18 crimps per inch and heatset for 20 minutes at C. The heatset tow was opened and made into 24.8 x 102 mm. filter rods with and without binder. The samples with binder were made by spraying the opened tow with 10% solids from a 25 solids polyethylene wax emul- Rod identification Hardness Pressure drop No binder, no heating 19. 4 12. 1 binder, no heating 11. 7 14. 8 10% binder heated, 10 mm. at

The bonded rods were easier cut and produced a cleaner out than did the unbonded rods.

Example X Twenty d./f. regular cross-section polypropylene yarn was wound into 60,000, 65,000, and 75,000 total denier skeins and crimped. Samples of tow were crimped at 12 and 18 crimps per inch using approximately 10 p.s.i.g. steam. One set of tows (60,000 and 75,000 denier) was heatset for 5 minutes at 125 C. without drying. The second set of tows (65,000 denier) was dried at 90 C. and then heatset for 5 minutes at 125 C.

The heatset tows were opened by hand, sprayed with approximately 5% binder from an approximately 25% solids polyethylene wax emulsion and made into 24.8 mm. x 102 mm. rods.

Rod samples containing polyethylene wax and amorphous polypropylene were made from the 60,000 denier tow while 75,000 denier tow was bonded with polyethylene wax alone. The polyethylene wax was applied from a food grade emulsion.

These rods were bonded by heating for 3 minutes at 110 C. Unheated rods were also checked.

The second set of tows (65,000 total denier dried and then heatset) were sprayed with 5% of polyethylene wax emulsion. Rod samples from this group were heated for 0.50, 1.0, 3.0, and 5.0 minutes at 110 C. and 125 C. to effect bonding.

All rod samples were checked for hardness and pressure drop.

The polyethylene wax appeared to give a harder rod than the amorphous polypropylene. The amorphous polypropylene bonded rods had hardness values of 16.00 and 21.8 for the heated and unheated samples respectively. The hardness values for the heated and unheated polyethylene treated rods were 6.9 and 13.0 respectively.

Complete data for the above are shown in Table I hereinafter.

The second group of rods was bonded by a polyethylene wax treatment consisting of a bonding time-temperature series. Rod hardness increased with both increasing time and temperature. After 5 minutes bonding time the rod hardness appeared to level 011. After /2 minute at 125 C. the 12 and 18 c.p.i. (crimps per inch) samples had hardness values of 5.9 and 8.2 respectively. The higher crimp level appeared to give slightly softer rods.

These data indicate that the pressure drop may decrease as the bonding time and temperature increase.

The second group of rods was dried at 90 C. and then heatset for 5 minutes at 125 C. This technique stabilized the polypropylene to the extent that it did not shrink when the filter rods were bonded.

Complete data on the time-temperature bonding series are shown in Table II, following.

TABLE I.BONDING OF POLYPROPYLENE FILTER RODS Tow Filter rod properties Heatsetting Rod bonding Hardness Pressure drop in water (inches) Fiber Total Crimpsl Time, Temp, Percent Time, Temp, Standard Length, d./f. denier inch mm. O. Binder binder min. C. Avge. Range deviation mm. Avge. Range 20 60,000 12 5 125 25% solids, 20 None None 13.0 3. 0-23.3 5.4404 102 3.40 2.9-4.3 polyethylene Wax emulsion 12 5 125 ...do 20 3 110 6.90 21.3-11.8 1.7255 102 3.07 2.3-4.6 12 5 125 25% solids, 20 3 110 16.0 3. 4-25.? 4.5269 102 3.50 2.7-4.5

amorphous polypropylene emulsion. 12 5 125 o 20 None None 21.8 12. 8-269 2.8623 102 3.43 2.5-4.5 12 None None None None None None 15.0 4. 6-19.1 5,5932 102 3.51 3. 0-45 12 None None 25% solids, None None 16.5 65-224 5.8830 102 4.93 4.4-6.2

polyethylene wax emulsion. 12 None None .-do 20 3 110 8.9 51-146 3,5150 102 4.77 3.8-5.4

TABLE II.-EFFEOT OF TIME AND TEMPERATURE ON BONDING OF POLYPROPYLENE FILTER RODS Tow Filter rod properties Heatsetting Rod bonding Hardness Pressure drop in water (inches) Fiber Total Crirnps/ Time, Temp. Percent Time, Temp, Standard Length, d./f. denier inch min. C. Binder inder min. C. Avge. Range deviation nun Avge. Range 20 65, 000 12 5 125 25% solids, 6 110 9. 2 5. 6-16. 0 1. 998 102 4. 80 3. 4-6. 4

polyethylene wax emulsion (sprayed). 12 5 125 "do 5 1 110 12. 3 6. 0-18. 8 3. 104 102 4. 87 4. 3-6. 3 12 5 5 3 110 5. 6 3. 5-14. 0 1. 538 102 4. 3. 7-5. 7 12 5 5 5 110 4. 4 2. 7-7. 6 l. 313 102 4. 3. 7-6. 0 12 5 5 /2 125 5. 9 3. 4-11. 9 1. 873 102 5. 25 4. 5-5. 9 12 5 5 1 125 6. 2 2. 8-9. 0 1. 928 102 4. 87 4. 0-5. 6 12 5 5 3 125 4. 7 2. 7-9. 2 1. 481 102 4. 88 4. 1-5. 6 12 5 5 5 125 4. 6 2.8-5. 7 0. 934 102 4. 4. 1-5. 8 18 5 5 6 11. 2 4. 2-18. 2 3. 273 102 5. 63 3. 9-7. 3 18 5 4 1 110 9. 1 4. 2-15. 2 2. 371 102 5. 71 4. 2-7. 5 18 5 5 3 110 6. 4 3. 8-12. 5 1. 984 102 5. 41 4. 7-6. 8 18 5 5 5 110 4. 3 3. 0-6. 0 0. 827 102 5. 08 4. 5-6. 3 18 5 5 8. 2 4. 5-11. 5 1. 481 102 5. 69 4. 5-7. 0 18 5 5 1 125 8. 2 3. 5-13. 1 3. 055 102 5. 41 3. 8-7. 0 18 5 5 3 125 5. 3 2. 5-10. 0 1. 988 102 5. 36 4. 1-6. 6 18 5 5 5 125 4. 1 2. 3-6. 7 1. 149 102 5. 19 4. 0-6. 5

7 Example XI A d./f. 30,000 total denier polypropylene tow was crimped to 16-18 crimps per inch. Approximately 5 p.s.i.g. steam was used on the crimper. The crimped tow was heatset in an oven for 20 minutes at 120 C.

Two ends of heatset tow were opened by hand, sprayed with a 25% solids polyethylene wax emulsion, and made into 102 mm. X 24.8 mm. rods. Rod samples were made at approximately 5%, and by weight of polyethylene. A sample of rods without binders was made as a control. Samples of rods from each polyethylene concentration were heated in an oven for 10 minutes at 95 C. and 110 C. The heatset, unheated and control rods were tested for hardness and pressure drop. Seventeen mm. tips were cut from each set of rods and checked for pressure drop and total removal.

Complete results are shown in Table III, which follows.

be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. The process of preparing a polypropylene vapor permeable bonded fibrous product which comprises gathering about 1 to denier per filament polypropylene into about 20,000 to 80,000 total denier two, crimping said tow at about 10 to 20 crimps per inch using 5 to 15 p.s.i.g. steam, heatsetting the thus crimped tow for at least about 5 minutes at about 90 to 150 C., opening the thus crimped and heatset tow, spraying said tow with a polyethylene wax emulsion of about 15 to 50% solids concentration, forming the sprayed tow into a rod-shaped member, and heating said member for at least thirty seconds at 90 to 150 C. to rigidly bond the fibrous vapor permeable filaments.

2. The process of claim 1 wherein prior to heatsetting the tow is dried.

TABLE III.BONDED POLYPROPYLENE FILTER RODS Rod Tip Pressure Pressure drop Drop Percent Fiber Crimps Percent Length, in water Hard- Length, in water removal identification per inch Binder binder Curing conditions mm. (inches) ness mm. (inches) total 5 D/F polypropy- 16-18 solids, 5 None 102 13. 3 14. 7 17 2. 89 25 lene 60,000 total polyethylene denier. wax emulsion (sprayed). D0." 16-18 (10 5 10 min. at 95 C. 102 10. 9 10. 0 17 2. 22

in oven. 5 10min. at 120 C. 102 9. 2 4.3 17 1.93 17 111 Oven. 10 None 102 14.8 11.7 17 2.67 31 1o 10 min. at 95 0. 102 11.6 6.9 17 2. 4e 25 I11 oven. 10 10 min. at 110 0. 102 8.9 2. 3 17 1.88 15 In Oven. 15 None 102 20. 7+ 8. 3 17 4. 36. 5 15 10 min. at C. 102 17. 6 3.2 17 3.85 25.5

in OVER. 15 l0 min. at 0. 102 10. 3 1. 9 17 1.96 55 111 oven. Do 16-18 None None None 102 12.1 19.4 17 2. 53 22.5

When staple fibers are used the staple length of the References Cited polypropylene which may be bonded with polyethylene UNITED STATES PATENTS fibers in accordance with our invention may be varied, for example from 1-10 inches. The polyethylene used as the 3339308 6/1962 Par me1e 15620O bonding medium may be produced by conventional melt 45 3,099,594 7/1963 et extrusion techniques as well as the method of our co- 3,110,642 11/1963 HaFmgton et a1 15628 pending application Ser. No. 54,929 now U.S. Patent 3,144,025 8/1964 Erhch No. 3,110,642. The polyolefins referred to above and the polyolefins used in the above examples are commercially available. They may be prepared, for example, as disclosed in our co-workers Patent U.S. 2,835,659.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can EARL M. BERGERT, Primary Examiner D. J. FRIT SCH, Assistant Examiner U.S. C1. X.-R. 15 61 80 

